Abrasive disk



April 21, 1925. 1,534,861

, H. c. MARTIN ABRAS IVE DISK Original Filed Jan. 25,-1922 I Patented Apr. 21, 1925.

UNITEDTSTATESV PATENT OFFICE.

HARRY C. MARTIN, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO 'IHE CARBORUN- DUM COMPANY, 01 NIAGARA FALLS, NEW YORK, A CORPORATION OF PENNSYL- VAN IA.

citizen of the Dominion of Canada, residing.

at Niagara Falls, Niagara County, New York,

provement in Abrasive Disks,'of which the following is ,a full, clear, and exact description, reference being had to theaccompanying drawings, forming part of this specification, in which. a

Figures 1 and 2 are sectional views of mold devices and illustrating steps in the manufacture of the abrasive disks; and

Figure 3 is a perspective view of a finished disk embodying my invention.

This application is a division of my pending application, Serial No. 531,554, filed January 25, 1922.

My invention relates to an improvement in abrasive disks, these disks being of the character used on machines known as disk grinders,'for grinding flatsurfaces on metals and other materials. Suchdisks usually consists of a paper or cloth backing or body coated with a thin layer of abrasive by means of glue af er the ordinary manner of sand paper and emery cloth. Their useislimited by the fact that the coating is relatively thin, and they do not possess very 'much durability when called upon to do heavy work. Their usefulness is also to a large degree conditioned upon the degree of porosity of theabrasive, the porosity being the measure-of the free cutting properties of the material. This is due to the fact that the degree of porosity controls freedom from glazing in use; or in other words, the free cutting properties of the disk depend upon the extent to which the material ground off is kept from lodging in the pores of the cutting surfaces.

have discovered that a very efficient abrasive disk can be made by building up an abrasive body consisting of abrasive grains bonded together by a resinous cement, preferablyof shellac, upon a backing of cloth or paper. I

In the practice of'my invention, for example in the making of a shellac disk, I employ a shallow circular mold consisting of an iron bottom plate 2 and aniron ring 3 of. the proper diameter required for the disk.-

In this mold, I placea disk 4: of cloth or paper and spread over this'a thin layer from three-sixteenths of an inch to three-fourths have invented .a new and useful Im- ABRASIVE DISK.

Original application filed .Tanuary 25, 1922, Serial No. 531,554. Divided and 30, 1924, .Serialno, 689,431.

this application filed January of an inch thick of abrasive grains mixed with powdered shellac, preferably in approximately the proportions by weight. of ninety-two parts abrasive grains and eight parts powdered shellac, although the exact proportions may be varied somewhat to meet the characteristics desired in the particular disk being manufactured. The shellac should, in general, not exceed nine or ten per cent of the mix, as shellac in excess of this makes the disk too hard and dense.

The mold with its contents is then placed in the melting oven and brou ht up to a temperature sufficient to bring t e shellac to a molten or plastic condition. The mold is then taken from the oven and a circular iron" plunger, such as illustrated at 5 in Figure 2, is inserted in the ring 3 upon the abrasive material, and the latter is subjected to pressure of three hundred to five hundred pounds, per square inch, which compresses and. ag-

glomerates it. Increasing the proportion of shellac and the pressure increases hardness and decreases the porosity of the disk. I have used in practice from eight to ten per- If the baking temperature does not exceed three hundred degrees Fahrenheit, the paper or cloth backing is not destroyed and is available for the purpose of forming an intermediate layer between the disk and the plate upon which the disk is fastened, when put into actual use.

As a modification of the above described method, I may, however, bake at a temperature .of three hundred and fifty degrees Fahrenheit. This temperature destroys the backing, but toughens and improves the abrasive. I then take a fresh piece of backing material and shellac it on to the abrasive disk by means of freshly melted shellac. In this manner, I obtain a combination of the shellac body and backing in as good a working condition as if the backing was originally incorporated with the shellac body.

It will be understood that the backing serves two functions, viz., it. acts as a means cent of shellac and hzwe varied the agglomof holding and carrying the disk body in its first melted condition and to strengthen the same until it is transferred to the baking operation, where it is toughened until it no longer needs such reinforcement. The second functions is to form an intermediate layer between the disk and plate, as above stated. Both these functions may be performed by the modification above described, as well as by the first described method.

I have found that disks made in accordance with my invention, using ordinary artificial aluminous abrasives in grits from No. 16 to No. 36, will weigh from 1.9 to 2.3 grams per cubic centimeter. The apparent density of two grams per cubic centimeter gives a very good cutting efficiency, and the disk does not glaze up with the material being ground, but maintains a very good cutting surface. With apparent densities of from 1.9 to 2.3 grams per cubic centimeter, the equivalent porosity varies from L7 to 36 percent; and it is important that the porosity should not be less than 36 percent, in order to give the free cutting properties above described.

An ordinary shellac bound grinding wheel made up according tothe methods heretofore in use with grits of these sizes and grades, has an apparent density of from 2A to 2.6 grams per cubic centimeter, and if used in the same cutting operation would very quickly glaze and show very poor cutting efiiciency.

In making such grinding wheels the amount. of shellac and the agglomerating pressure greatly exceed that employed in making my grinding disks. f

In addition to the increased porosity, the disks made in accordance with my invention have a uniform texture throughout so that they will remain eflicient during their life. They also possess the advantage'that they do not crack or chip at the edges. They may be used either wet or dry, which is not true of a glued disk. The disks may be made of any desired grade of hardness to suit the particular work in which they are to be used.

While thedisks have sufficient porosity to prevent glazing, they have suflicient strength and density to stand up under hard usage, and have a' durability and cutting efficiency much greater than disks made of al rasive material not compressed The disks may also bobuilt up to any thickness esired,

eral ,speeds than disks having weaker' bonding materials, such for example, as magnesia cement. The abrasive composition of the disks is considerably more porous, and hence, structurally not as strong as the more dense shellac bound abrasive Wheels containing a greater percentage of shellac and made with a higher agglomerating pressure. However, the cloth backing of my disks supplies an added tensile strength, so that the composite disks are capable of safely operating at the high peripheral speeds now used in disk grinding. The disks, therefore, combine high enough p0- rosity to prevent glazing, sufficient thickness, strength of bond and density to have great durability, and the necessary tensile strength for high speed grinding machinery.

W'hile I have described in detail the preferred embodiment of my abrasive disk and its process of manufacture, it is to be understood that the invention is not limited to all of the described details, but may be otherwise embodied withinthe scope of the following claims.

I claim: 1. An abrasive disk comprising a backing of flexible material and an abrading portion built up of abrasive grains and a resinous bonding material and having a porosity of not less than 36 substantially as described. 2. An abrasive disk comprising a backing of flexible material and an abrading portion built up of abrasive grains and a resinous bonding material and having a porosity in excess of 40%, substantially as described.

3-. An abrasive disk comprising a flexible backing and an abrading portion formed of a compressed mixture of abrasive grains and with not over 10% of shellac as a bonding material, substantially as described.

4. An abrasive disk comprising a flexible backing and an abrading portion formed of a compressed mixture of abrasive grains and with 8 to 9% of shellac as a bonding material, substantially as described.

In testimony whereof I have hereunto set my hand.

' HARRY o. MARTIN. 

